1. Field of the Invention
This invention relates to a decoding apparatus for transmission equipment for transmitting or recording digital picture data with the data compressed through highly efficient encoding.
2. Description of the Prior Art
In one method of encoding to decrease the picture data is converted into a two-dimensional or three-dimensional block structure and compressed and encoded in every block. The two-dimensional block is formed by segmenting one field or one frame, while the three-dimensional block is formed as an assembly of two-dimensional blocks respectively belonging to plural frames which are continuous in time. Encoding of the two-dimensional block has an advantage in that the circuit size is small, while the encoding of the three-dimensional block has not only the advantage that improved efficiency can be achieved but also an advantage that a decoded still picture has high quality.
Further, encoding which combines subsampling and block encoding is known. With such encoding, highly efficient compression can be achieved. In particular, a system in which the phase of subsampling varies with every frame can attain compression without degradation of definition of a still picture by the use of interpolation over time.
The transmission side of such an encoding apparatus is equipped with a subsampling circuit, a block segmentation circuit for converting the order of input data into a three-dimensional block structure, and an encoder for block encoding, and a buffering circuit is provided so that the data generated for a predetermined period (for example, one frame period) by the encoder does not exceed the capacity of the transmission path. On the reception side, a decoder of the block encoding, a block desegmentation circuit for converting the three-dimensional block structure into the scanning order, and an interpolating circuit for interpolating non-transmission picture elements thinned out in the subsampling are provided.
In a conventional encoding system where the subsampling and the encoding of the three-dimensional block are combined, the block segmentation circuit requires a two-frame memory, and the buffering circuit needs also two-frame memory for delaying picture data. Similarly, on the reception side, a two-frame memory for block desegmentation and a two-frame memory for interpolation are needed. Consequently, an eight-frame memory is needed in total for the transmission side and the reception side, which presents a problem in that the size of the required hardware becomes large.